I added to my current house and now my aerobic system is too small. I was told that I can convert conventional system using the same/existing aerobic tank to get more capacity. I have three questions:
1) Can I really use the same tank?

2) If its "yes" for 1), will it be the same capacity as an conventional tank of the same size?

3) I was told that two 750 gals tanks should be able to support 11 bedrooms, 9100 square feet living space, 12 full baths. Is this true?

Where do you live? In my locale we require 1500 gallon tanks for just 4 bedrooms. Call you local building inspector and ask about what they require, it varies from state to state